Over the past several years there have been continuing attempts to improved specific properties of cellulosic pulp-derived products by utilization of a variety of debonding agents. These debonding agents quite frequently include a quaternary amine component because of the high degree of substantiveness of this moiety for cellulose. Examples of quaternary amine debonders can be found in U.S. Pat. Nos. 3,554,863; 3,554,862; 3,395,708; and No. Re. 26,939 issued to Laurence R. B. Hervey, et al. Additional examples of such debonders can be found in U.S. Pat. No. 3,617,439 issued to Benjamin E. Chapman, Jr., Canadian Pat. No. 1,020,935 issued to Louis S. Hurst, et al, British Pat. Nos. 1,282,593 and 1,180,801 also issued to Hervey, and U.S. Pat. Nos. 3,556,931; 4,510,246 and 3,356,526.
Until fairly recently it has been axiomatic in the pulp and paper industry that the debonding function was inversely related to hydrophilicity, i.e. the increase in efficiency of debonding as represented by reduced physical strength would result in reduced absorbent rate and total absorbent capacity in subsequent product applications of the pulp.
Typical debonders are long chain cationic surfactants, preferably with at least 12 carbon atoms in at least one carbon chain. Specific non-limiting examples of these would be fatty dialkyl quaternary amine salts.
The mechanism for debonding with these materials occurs as follows. The polar quaternary portion of the surfactant is strongly attracted to the negatively-charged cellulose fibers. It is this strong electrostatic interaction which leads to the excellent substantivity of the quaternary amine molecule for the cellulose fibers. This interaction leaves the hydrophobic portion of the surfactant molecule exposed thus giving the fiber surface hydrophobic properties, which interferes with the ability of inter-fiber bonds to form resulting in decreased physical strength of the pulp. This hydrophobic surface on the cellulose fibers also results in a pulp which exhibits increased hydrophobic behavior relative to the same pulp without the surfactant. In applications for highly absorbent products the increased hydrophobicity of the treated pulp is unsatisfactory.
U.S. Pat. No. 4,144,122 issued to Jan G. Emanuelsson, et al discloses a class of quaternary amine compounds containing repeating hydrophilic ethylene oxide units at two of the quaternary positions. These ethylene oxide units are attached to the quaternary nitrogen by propylene linkages in each case. They are also characterized by an ether linkage to an aliphatic chain at both positions. According to U.S. Pat. No. 4,144,122, debonding is accomplished while the hydrophilic character of the debonded pulp is improved when compared with conventionally debonded pulps. This relatively improved hydrophilicity is due to the reduction of the hydrophobicity of the alkyl chains due to the presence of the ethylene oxide units. Now, when the interaction of the cationic quaternary amine and the anionic cellulose fibers occurs, the portion of the molecule exposed is of decreased hydrophobicity, and the cellulose fiber surface of improved hydrophilicity, relative to that found for conventional debonders.
According to this invention, another class of debonding compounds has been identified which produces pulp which is more hydrophilic than the pulp produced according to U.S. Pat. No. 4,144,122. The compounds used in this invention use hydrophobic components of the quaternary amine as separate moieties from the hydrophilic components.
When the quaternary amine used in this invention interacts with cellulose fiber, reduced inter-fiber bonding again occurs. However, with the compounds utilized herein, both hydrophobic and hydrophilic portions of the molecules are exposed resulting in a cellulose fiber surface of hydrophobic and hydrophilic regions. Unexpectedly, this results in a pulp of greatly improved absorbent properties. While the applicant can not completely explain the mechanism by which the presently disclosed compounds accomplish their beneficial action, and further does not wish to be bound by theory, it is likely that as the cellulose fibers come into contact with the liquid to be absorbed, a hydrophilic pathway is always presented by which formation of the absorbing liquid-cellulose fiber interface can be accomplished more easily than if only a hydrophobic cellulose surface was presented. That the class of molecules described by this invention achieve hydrophilic debonding by a more efficient mechanism than occurs for the class of molecules described by Emanuelsson is clear when a compound used in this invention is directly compared with a compound which is structurally similar but covered by the Emanuelsson patent as shown in Example 4. In each case the molecules described by this invention are superior.